Guard for grinding or polishing wheels



May 15, 1956 o. M. KROGSGAARD GUARD FOR GRINDING OR POLISHING WHEELS 2 Sheets-Sheet 1 Filed Nov. 8, 1954 May 15, 1956 o M. KROGSGAARD 2,745,230

GUARD FOR GRINDING OR POLISHING WHEELS Filed Nov. 8, 1954 2 Sheets-Sheet 2 United States Patent GUARD FOR GRINDING 0R POLISHING WHEELS Olav Marius Krogsgaard, Aarhus, Denmark Application November 8, 1954, Serial No. 467,527

' 7 Claims. (Cl. 51-270 The invention relates generally to grinding or polishing wheels and more particularly to a guard connected therewith.

The known guards of this type do not fulfill their object, i. e. to catch the grinding particules flung away from the wheel, in a satisfactory manner. The powder flung away from the wheel soils the operator, as well as the working table, and additionally, if the powder is dry, it will fill the air of the room with dust, which in many cases will cause unhealthy eifects.

In some instances suction guard aggregates have been used, but such devices are expensive to provide and, if they are to be effective, they suck great quantities of warm air away from the room so that the expenses in connection with the heating of the room are essentially increased.

It is the object of the present invention to remedy'these shortcomings by providing a guard which prevents the ejection of grinding particles far more than the guards hitherto known, irrespective of whether dry or wet grinding powder is used. The characteristic feature of the guard, according to the invention, is that it is provided with an aperture substantially opposite the working place, and that it has between the guard and the periphery of the wheel a guiding plate, one end of which is positioned in or adjacent the aperture, and the other end of which is located at the end of the space between the guard and the wheel limited by a concave front end wall.

This construction results in the greater part of the grinding dust being flung out through the aperture at the rear wall of the guard, and this aperture may in a suitable manner be connected to a dust separating apparatus or discharge container. The part of the grinding dust carried around to the front end wall is also directed by the guiding plate to the rear of the guard as it is carried along by the air current produced by the rotation of the wheel. The channels formed around the guiding plate may be advantageously connected to a dust separating apparatus or a separate discharge container. Thus, the same effect has been obtained, which was hitherto only obtainable when using special ventilators or other means for the production of air currents and with far less or entirely without extra use of hot air.

The simplest and cheapest construction, according to the invention, may be obtained by arranging the guiding plate in such a manner relative to the aperture that the opening limited by the lower part of the guiding plate and the upper edged the aperture has substantially the same area as the cross section of the channel limited'by the guard plate and the guiding plate.

Furthermore, according to the invention, it may be preferable that the front end wall is partially constituted by a portion of the guard which is adjustably arranged in such a manner that it may overlap the edge of the sta tionary part of the end wall more or less. Thestationary part of the guard and the movable guard portion may then be dimensioned in such a manner relative to the grinding wheel or polishing wheel that the whole guard, when the movable guard portion has been pushed up, may be drawn "ice backwards over the wheel for ready access to the wheel, such as when replacement is necessary. When the guard is used, the movable guard portion is adjusted in such a manner that its lowermost edge almost contacts the wheel.

In order to make the guard better suited for use when grinding with wet grinding powder, it may'preferablybe provided with a gate which is movably arranged in such a manner that it can be operated to close the opening in the rear side of the guard so that the grinding means will remain inside the guard.

According to the invention the screen need not be connected to a separate discharge container in order to fulfill its object, but the dust carried away by the air currents must be separated in some type of a suitable apparatus which allows the air to pass but retains the grinding particles.

According to the invention such a dust separating apparatus, has the shape of a container which at its front end is arranged for connection with the aperture in the guard, and which has an inwardly concave rear wall of substantially spiral shape with approximately one whole spiral turn, while between the spiral and the front end the container is provided with an upwardly turned opening.

This construction of the dust separating apparatus results in whirls of air being formed in the rear part of the apparatus. From these whirls the heavier grinding particles will fall down and are deposited onthe bottom of the apparatus while the air will flow out through the uncovered portion of the upper side of the apparatus.

The invention will be further described in the following specification with reference to the drawing, in which Figs. 1 and 2 are a side elevation and a sectional view, respectively of an embodiment of a guard arrangedaround a polishing wheel and connected to a dust separating apparatus according to the invention, the gate being left open,

Fig. 3 is a sectional view of the guard with the gate closed, I

Fig. 4 is a front view of the guard showing the polishing wheel connected with an associated motor,

Fig. 5 is a sectional view of another embodiment of the dust separating apparatus made in one'piece with the guard, and Y Fig. 6 is a preferred construction and location of the gate which can beadapted to close the opening in the rear side of the guard. l

The embodiment illustrated in Figs. l to 4 of the guard and the dust separating apparatus according to the invention is particularly contemplated to be used in connection with such polishing wheels as are used in dental laboratories, e. g.'for the polishingof prothesis, but may,

of'course, also be used for many other forms forpolish-f ing or grinding wheels.

The polishing wheel or brush, which in the drawing is designated by 1, is mounted on a shaft 3 of a rotatable electric motor 2. The guard itself consists substantially of a'plate 4 formed with a cylindrical surface and a conple of plane parallel side members 5. The side member 5 which faces the motorwhen the guard is in position-- wardly concave front endwall'lt), which, if desired, may

extend practically right'up to the periphery of the wheel but the inner edge of which is positioned in the illustrated embodiment in such away that the whole guard may be drawn rearwardly out over. the wheel. Since the desired effect of the guardtocatch the grinding particles is de pendent on the fact that the end wall extends substantially right up to the wheel, a guard portion 11 is pivotally mounted on pins or rivets 12, and when in use the guard portion 11 is adjusted in such a manner that its inner edge lies as close as possible to the wheel 1. The guard portion 11 is provided with an operation button 13 for readily imparting the necessary pivotal movement. As mentioned hereinbefore, end wall 10 is constructed so that the entire guard unit may be withdrawn rearwardly from the wheel 1, and at the time such withdrawal is made, it should be understood that guard portion 11 is pivoted counterclockwise to its uppermost position to provide proper clearance.

The rear side of the guard wall 4 with the cylindrically shaped surface, approximately at a level with and opposite the working place 9, is provided with an opening 14, and between the guard wall 4 and the wheel 1 there is positioned a guiding plate 15, the lowermost and rearrnost edge of which is located adjacent the opening 14 which it intersects. From its rearmost edge plate 15 extends upward and forward to a chamber formed between the wheel 1 and the guard wall 4 which is located immediately above the working place 9. It is seen that the concave portion 11. extends both above and below the forward edge of guiding plate 15. Thus, the guiding plate 15 together with the grinding wheel 1 form an upwardly and forwardly extending first channel, designated in Fig. 2 by a forwardly extending arrow above grinding wheel. A curved or U-shaped channel is formed between the concave portion 10 and the forward edge of plate 15, and a second channel 19 extending downwardly and rearwardly to opening 14 is formed between plate 15 andguard wall 4. Along its front edge the guiding plate 15 is-formed with a portion of expanded thickness 16.

A gate 17 is formed and guidable in a pair of rails 18 fastened to the outer side of the guard portion 4. When moved to'its topmost position as shown in Figs. 1 and 2 gate 17 is positioned atop guardwall 4 and opening 14 is thereby uncovered to allow grinding particles to pass therethrough. However, when gate 17 is moved to its lowest position as shownin Fig. 3, opening 14 is thereupon covered.

The gate 17 may also be hinged to the guard wall 4 so that it can be pivoted instead of displaced to cover or uncover opening 14.

The lower part of the guard may be fitted in a manner well known in the art with an extension 20 forming a tray for the collection'of the grinding particles. In Figs. 1, 2- and 3 the guard is shown with tray 20 mounted on a table top 21.

When the illustrated and described guard is to be used in connection with polishing or grinding with dry grinding powder, the gate 17 is pushed up into the position shown in Figs. 1 and 2 so that the opening 14 is uncovered. The greater part of the dust laden air fromthe under side of the wheel is then discharged through the lower part of the opening, as shown by the arrow 22 in Fig. 2. However, part of the dust laden air will be carried around the wheel up along the underside of the guiding plate 15 and into the'charnber between the Wheel and the guard immediately above the working place 9; At this point the air current is deflected by the concave end wall 10 and continues in a rearward direction out through the channel 19 between the guiding plate 15 and the guard wall 4 so as'to eventually flow out through the' upper part of the opening 14. That part of the air current which is indicated by the arrow 23 in Fig. 2 is made slightly stronger by the. injector effect created by the main current-shown by arrow 22 flowing through opening 14.

It is thereby seen that the grinding particles which would normallybeejectediforwardly from under the front edge of the guard are shownin" thezpresent invention to becarried along. by thez'rearwardly moving air currents illustrated. byarrows:22- and 23=out.through the opening 14. The opening. 14 may preferably be connected to a discharge container or a suitable dust separating apparatus thereby making it possible to avoid having the air of the room polluted by grinding particles.

When the gate 17 is pushed down so that it closes the opening 14 as shown in Fig. 3, the guard, according to the invention, may be used to' grind or polish with wet grinding powder. The wet powder will then be deposited along the rear'side ofthe guard from where it may later on be pulled out on the tray 29 and used again.

In Figs. 1 and 2 the guard is shown as being connected to a dust separating, apparatus 24. In this embodiment of the invention the air is allowed to pass through the separating apparatus 24, but the grinding particles are retained therein. The apparatus 24 has the form of a container which at its forward end is adapted to be connected to the opening 14' of the guard as shown in Figs. 1 and 2. Therear wall 25 of apparatus 24 is inwardly concave and substantially shaped as a spiral so as to include one entire convolution starting at the point A and terminating at the point B. Immediately forward of the point of termination B of the spiral the apparatus 24 has anupwardly turned opening 26' as shown in Fig. 2.

Theoperation of the dust separating apparatus is based on the fact that the dust laden air currents shown by arrows 22 and 23 unite into one single current upon being forced through the opening 14 by the rotation of the wheel, and this single current is formed into a whirl by the spiral construction of apparatus 24. From this whirl the grinding particles will gradually sink down to the bottom of the apparatus 24, whereas the air will escape upwardlythrough the opening 26.

The illustrated and described embodiment of the guard according to the present invention is especially intended foruse in catching grinding particles in dental laboratories. For practical reasons, a guard for this purpose must be constructed comparatively broader in dimension than the grinding or polishing wheel, as appeared from Fig. 4, and such construction has resulted in the desired effect to a satisfactory degree. However, it should be noted that this desired effect can be even more emphasized if it is possible to construct the guard of approximately the same width as the wheel, whereupon the active currents of air would become more intensified'and efficient to direct the grinding particles rearwardly.

In Fig. 5 another embodiment of the guard and the dust separating apparatus according to the invention is shown, in which the two parts are made of one piece. At the Working place 9' is shown a blank 30. In the rearmost part of the dust separating apparatus the bottom of the container 24 of which the apparatus consists, is constituted by a grate 31 having a series of bars that are shaped of obliquely positioned transverse lamellas 32. As shown the lamellas' 32 are arranged in such a manner that their front edges are disposed lower than their rear edges. The whole dust separating apparatus is enclosed in a casing 33 in the bottom of which there is a drawer 34 with a handle 35. Instead of having the dust deposited on flte bottom of apparatus'24'as shown in Figs. 1 to 4, whereupon the'dust could possibly be whirled up again by the air currents from the guard, the grinding dust will inthis' case fall down'through the grate 31 into the drawer 34' where it is essentially removed from the whirling influence of the air current. This embodiment will be very suitable for grinding plants of some magnitude.

It is also possible in this guard construction to mount vanes'on the sides of the grinding wheel 1' or on the shaft adjacent the wheel in'order to intensify the active currents of air.

In Fig; 6a special embodiment of the gate 17 and its: location is shown. At theforward and rearward edges of the gate there is fasteneda rod 36 and 37, respectively, the ends of which extend transversely beyond the gate to form guiding pins so'a's 'to-guideth'e gate-17' within the rails 18' inthe same way as shown in Figs. 1 to 4. When the gate is pushed up to its extreme forward'position, the rod 36 upon being pushed slightly more forward, can be disengaged from the rails 18. Gate 17 can then be pivotally swung about the rod 37 and positioned as shown in Fig. 6 to form a covering over the upper front part of the apparatus 24". In addition, a set of recesses 38 may be formed in the upper walls of apparatus 24" to'receive the ends of the rod 36. The downward displacement of the gate 17' may be limited as shown in Fig. 6 by providing a stop member 39 adjacent the bottom end of rails 18'.

Although the various surfaces guiding the currents of air are illustrated in the drawings as being constructed with soft curves in conformity with the ordinary aerodynamic principles, the desired effect will, however, also be obtainable, maybe to a smaller degree, by substituting these surfaces with a greater or smaller number of plane surfaces forming a more or less good approximation of the curved surfaces. This applies to the guard itself as well as to the dust separating apparatus.

l. A guard for a grinding wheel comprising a guard wall adapted to substantially enclose said wheel along its periphery to control the flow of grinding particles carried in the air current produced by rotation of said wheel, saidguard wall having a front end wall positioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed at the same level as and substantially opposite said working place, a guiding plate having one end thereof positioned substantially within said aperture and extending forwardly therefrom with the other end terminating adjacent to said front end wall, 'said front end wall having an inner concave portion extending above and below the front end of said guiding plate, said guiding plate being adapted to form a first channel'between said guiding plate and said grinding wheel, ascurving channel between said concave portion and the front edge of said guiding plate and a second channel between said guiding plate and said guard wall, said grinding wheel being mounted for rotation and adapted to direct part of the air current rearwardly below said grinding wheel and through said aperture and to direct the other part of the air current forwardly through said first channel, around through said curved channel, rearwardly through said second channel and through said aperture, and said second channel having approximately the same area as the upper part of said aperture formed between said guiding plate and said guard wall.

2. A guard for a grinding wheel comprising a guard wall adapted to substantially enclose said wheel along its periphery to control the flow of grinding particles carried in the air current produced by rotation of said wheel, said guard wall having a front end wall positioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed therein on a level with said working place, a guiding plate having one end thereof positioned substantially within said aperture and extending forwardly and upwardly therefrom with the other end terminating adjacent to said front end wall, said front end wall having an inner concave portion extending above and below the front end of said guiding plate, said guiding plate being adapted to form a first channel between said guiding plate and said grinding wheel, a U- shaped channel between said concave portion and the front edge of said guiding plate and a second channel between said guiding plate and said guard wall, said grinding wheel being mounted for rotation and adapted to direct part of the air current rearwardly below said grinding wheel and through said aperture and to direct the other part of the air current forwardly through said first channel, around through said curved channel, rearwardly through said second channel and through said aperture, and a gate part mounted on the outer side of said guard wall and adapted for sliding engagement along said guard wall to selectively cover said aperture.

3. A guard for a grinding wheel comprising a housing portion having an opening in the front section thereof to receive said wheel and having a guard wall adapted to substantially enclose said wheel along its periphery .to control the flow of grinding particles carried in the air current produced by rotation of said wheel, said guard wall having a front end wall positioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed therein on a level with said working place and generally of the same size as said opening, said guard wall being spaced on either side of said wheel a distance at least as wide as the width of said wheel,'a guiding plate having one end thereof positioned substantially within said aperture and extending forwardly and upwardly therefrom with the other end terminating adjacent to said frontend wall, said front end wall having an inner concave portion extending above and below the front end of said guiding plate, said guiding plate being adapted to form a first channel between said guiding plate and said grinding wheel, a U- shaped channel between said concave portion and the front edge of said guiding plate and a second channel between said guiding plate and said guard wall, said grinding wheel being mounted for rotation and adapted to direct part of the air current rearwardly below said grinding wheel and through said aperture and to direct the other part of the air current forwardly through said first channel, around through said first channel, around through said curved channel, rearwardly through said second channel and through said aperture, a gate part mounted on the outer side of said guard wall and adapted for sliding engagement along said guard wall to selectively cover said aperture, and a tray attached to the lower part of said guard wall below said wheel and extending forwardly therefrom and adapted to receive grinding particles when said gate part covers said aperture.

4. A guard for a grinding wheel comprising a guard wall adapted to substantially enclose said wheel along its periphery to control the flow of grinding particles carried in the air current produced by rotation of said wheel, said guard wall having a front end wall positioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed therein on a level with said working place, a guiding plate having one end thereof positioned substantially within said aperture and extending forwardly and upwardly therefrom with the other end terminating adjacent to said front end wall, said front end wall having an inner concave portion extending above and below the front end of said guiding plate, said guiding plate being adapted to form a first channel between said guiding plate and said grinding wheel, a U-shaped channel between said concave portion and the front edge of said guiding plate and a second channel between said guiding plate and said guard wall, said grinding wheel being mounted for rotation and adapted to direct part of the air current rearwardly below said grinding wheel and through said aperture and to direct the other part of the air current forwardly through said first channel, around through said curved channel, rearwardly through said second channel and through said aperture, a gate part mounted on the outer side of said guard wall and adapted for sliding engagement along said guard wall to selectively cover said aperture, and a dust separating apparatus connected to said rearward section of said guard wall along the periphery of said aperture, said dust separating apparatus having a spiral shape to impart a corresponding spiral action to dust particles passing therethrough.

5. A guard for a grinding wheel comprising a guard wall adapted to substantially enclose said wheelalong its periphery, said guard wall having a front end wallpositioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed therein, a guiding plate having one end thereof positioned substantially within said aperture and extending forwardly therefrom with the othcr end termintaing adjacent to said front end wall, said guiding plate being adapted to form a channel between said guiding plate and said guard wall, a gate part adjustably mounted along the upper part of said guard'wall for selectively covering said aperture, and a dust separating apparatus including a housing connected to said rearward section of said guard wall along the periphery of said aperture, said dust separating apparatus being formed with a portion of spiral shape at its rear end and having an opening formed in the top of said housing between the spiral portion and the intersection of the guard wall and housing.

6. A guard for a grinding wheel comprising a guard wall adapted to substantially enclose said wheel along itsperiphery, said guard wall having afront end wall positioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed therein, a guidingplate having one end thereof positioned substantially within said aperture and extending forwardly therefrom with the other end terminating adjacent to said front end Aguard for a grinding wheel comprising a guard wall adapted to substantiallyenclose said Wheel along its periphery, said guard Wall having a front end" Wall positioned closely adjacent to the working place of said wheel and having a rearward section positioned remotely from said wheel with an aperture formed therein, a guiding plate having one end thereof positionedsubstantially within said aperture and extending forwardly therefrom with the other end terminating adjacent to said front end wall, said guiding plate being adapted to form a channel between said guiding plate and said guard wall, a gate part adjustably mounted along the upper part of said guard wall for selectively covering said aperture, and a dust separatingapparatus formed as a rearward extension of said guard' wall to receive grinding particles passing through said aperture, said dust separating apparatus having a single convolution formed at its rearward end' and a plurality of lamellas formed below said convolution in the lower part of said dust separating apparatus and obliquely positioned in a manner that the front edge thereof is lower than the rear edge.

References Cited in the" file of this patent UNITED STATES PATENTS 776,156 Venderbush Nov. 29, 1904 790,943 Weber May 30; 1905 956,762 Furr'ow May 3, 1910 1,174,659 Bilicki Mar. 7, 1916 1,357,308 Bertschin'ger Nov. 2, 1920 1,374,075 Graham Apr. 5, 1921 1,406,914 Virgilio Feb. 14', 1922 1,476,196 Dobyne Dec. 4, 1923 1,982,592 Dobyne Nov. 27, 1934 2,056,505 Dobyn'eet al Oct. 6, 1936 2,100,344 Medart Nov. 30, 1937 2,383,454 Eisler Aug. 28, 1945 2,557,207 Than-Jensen June 19, 1951 2,618,916 Ofteda'l Nov. 25, 

